[Reviewer: Mike] Add branch ID markers to SAS trails

Mike,

Please can you review this partial fix to issue #343?  It's currently untested but given the timezone difference I was hoping you could take a look at it first.

It should all be pretty self-explanatory, but one specific question I had was what the correct scope to use when reporting the marker.  I specified Branch as a guess, but it could easily be wrong - there doesn't seem to be much documentation of what this scope means.

(Obviously, please don't merge until I've live-tested.)

Thanks,

Matt